Replace the paramiko implementation with direct Popen calls for ssh

Paramiko is very strict about authentication, and we cannot figure out what configuration settings we must set in order to have ssh calls work with hosts that have properly configured keys. So we are replacing Paramiko with bare ssh calls from Popen.

this commit fixes #16 
I've read on stack overflow that if you exit the ssh command gracefully, then the nohup signal doesn't get invoked. If anything, I was considering having the ampersand as a part of the remote shell client class.

Actually, I still don't like that idea. It still feels somewhat 'magical'.